1. Field of the Invention
The present invention relates generally to micro-fluid ejection devices and fluid ejecting methods; and specifically, in an exemplary embodiment, to an inkjet printhead and an ink ejecting method using a laser to nucleate ink contained within a printhead so as to rapidly grow a vapor bubble which displaces a portion of the ink, thereby ejecting an ink droplet.
2. Background of the Invention
Typically, ink-jet printheads are used for printing a predetermined image by ejecting a small volume droplet of printing ink at a desired position on a recording media or substrate. In such inkjet printheads, ink ejection mechanisms are largely categorized into two types depending on which ink droplet ejection method is used. One type of conventional inkjet printhead is a thermally driven inkjet printhead in which a thin-film, heater stack based heat source is employed to form bubbles in ink to cause ink droplets to be ejected by an expansion force of the bubbles. This type of inkjet printhead has proven to be inefficient as large amounts of energy are required to boil the ink and form the bubbles. In addition, there is a limitation on the type of ink used.
In addition, other ink droplet ejection methods have been developed and are conventionally used in inkjet printheads. In one such conventional method, a piezoelectric crystal having a concave surface and a convex surface is installed under a surface of ink to be ejected. An electrode is provided on the concave surface of the piezoelectric crystal and three other electrodes are provided on the convex surface of the piezoelectric crystal. The piezoelectric crystal produces sonic energy, and an acoustic pressure generated by the sonic energy vibrates the surface of the ink. If the acoustic pressure exceeds the surface tension of the ink and atmospheric pressure, ink droplets are ejected from the surface of the ink through a hole in a passageway plate of the printhead. Selective combinations of electrodes are operable for controlling an ejecting direction of each of the droplets. Disadvantageously, the above described ejecting method presents a problem due to a complex structure thereof because the hemispherical piezoelectric crystal and the electrodes must be installed under the surface of the ink.
In another conventional printhead device, an ink droplet ejecting method using a laser is disclosed. Typically, a printhead is provided which includes a plurality of chambers containing multiple colored inks, a semiconductor laser for selectively irradiating a laser beam onto the inks, and a condenser lens which converges the laser beam. The laser beam emitted from the semiconductor laser is selectively irradiated through the condenser lens onto the inks contained in the chambers. Accordingly, the inks evaporate and the evaporating inks move to a substrate. This ink ejecting method, however, is disadvantageous in that control of the procedure is complex and a large amount of energy is consumed.
In still another conventional ink ejecting method, an ink ejecting method in which a buffered solution is boiled using a laser and the ink is ejected by vibrations caused by the boiling of the buffered solution is taught. This method has similar problems with the foregoing prior art in that the structure of the ink-jet printhead is complex and a large amount of energy is consumed.
In still another type of conventional ink ejecting method, a printhead is disclosed which causes the ink to vibrate through the use of a laser having a sufficiently high energy to generate a pressure wave which expels the ink. While this method avoids the need for boiling the ink, it requires an excessive heating cycle to elicit the density response necessary for expulsion.